A week ago, Inhabitat reader Bob Ellenberg contacted us, expressing frustration with all of the prefab housing companies jumping on the eco bandwagon and claiming their products are green simply because they are prefabricated. We thought he had a good point, so we are publishing his critique below. We’d love to hear your thoughts on the matter….

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PREFAB CONSTRUCTION: Green or Greenwashing? By Bob Ellenberg I don’t want to pick on prefab construction, as I do quite a bit of it myself as a design/builder and there are certainly many aspects of it that can be “green.” But some of the claims I see being made relative to overall sustainability of prefab houses are overstated and might even be considered “Green-Washing”. Let’s start with what is perhaps a debatable point–the fact that factories have a high overhead cost of operation compared to on-site building and in all probability a higher carbon footprint along with it compared to on site construction…

MATERIAL WASTE–This is one of claims I have the most problem with. One prominent prefab web site states, “Materials are ordered in such a way that there are only trace amounts of waste instead of the tons of debris produced building on-site.” and other websites make similar claims. Standardized materials are ordered by on-site builders and prefab factories alike. In fact, an on site builder will usually order the different lengths of lumber he needs for one particular job that produce the least amount of waste. A factory sometimes orders large quantities and pulls from their own inventory but they both buy the same size lumber that comes from the same mills.

“Extra materials in the factory can be stored and used on the next house as opposed to winding up in a landfill.” is another claim. If the above statement is true–what are factories storing their leftover materials? On some on-site jobs, the subcontractors don’t scrap out material as well as they should because they don’t get paid anymore for being frugal with the materials. By the same token, some factories have the same attitude because it cost them more in labor to have employees sort and use the scrap pieces than it cost them to cut up what is there at the work station and they save labor cost. On site can be as “green” in scrapping out material as a factory and a factory can be just as wasteful. The real question is how “green” the approach is of the people running the show.

OVER-ENGINEERING Factory produced modular homes often require more material than site-built homes, and this is definitely not green. When you build a house on site, you generally have a perimeter foundation and a slab on which you erect everything one piece at a time and the continuous foundation under those pieces hold them up. With a factory built house, you have to lift a large module, load it on a truck, haul it down the road and set it with a crane. Because all of these operations concentrate the load on specific points instead of it being spread as it is over a foundation or a slab, the support system must be considerably overbuilt. They typically use laminated veneer lumber (LVL) for perimeter floor bands that are doubled. In addition, some of the interior walls are usually doubled as the module must be closed in and give support for transport but then go back to back against another module when set in place. There will be variables but the factory built modular houses will always consume more materials than the same house built on site.

CARBON COST OF SHIPPING Shipping modular homes definitely adds to the carbon footprint as well. Truck loads of materials go to local suppliers, travel short distances to site built homes and stay there. Truck loads of materials go to factories, are built into houses and then travel hundreds of miles on oversized trucks with small trucks (called escort vehicles) running in front and behind while traveling through towns with police and local cars idling while traffic is stopped for them to go by. Then the crane which gets about 2-3 mpg travels to the job site to set the house and unless you are in a major city they could end up coming a long way.

Am I a foe of prefabricated houses? Absolutely not. I have designed them, erected and completed them and I live in one. In fact, I am designing some very green ones at the present time that I will be producing later this year. But I want to honestly question what is and what isn’t “green” about prefabrication and encourage others to do the same.

What do YOU think?


Bob and Karen Ellenberg have been designing and building homes since the early 70’s. They have built on-site wood frame homes, masonry structure homes, prefabricated modular homes and prefabricated kit homes. They have built in warm humid Southern climates and in high altitude cold dry Southwestern climates. They have built entry level homes and they have built award winning custom luxury homes and are known for their attention to detail. In addition Bob has worked extensively in damage assessment in the aftermath of hurricanes, earthquakes, fires and tornados which has given him additional insight into what really works not only in terms of safety but in repair costs as well. Few designers or builders have such broad hands on experience and knowledge. Bob can be contacted at [email protected]